1. Field of the Invention
This invention relates to a lens barrel having focusing and zooming motors.
2. Description of the Related Art
The actuators (motors) provided for driving the lens barrel of a compact video camera in focusing and zooming the lens have been disposed at a position where the optically designed lens diameter is small. More specifically, they have been disposed between a diaphragm position and an optical focus position (sensor position) for the purpose of minimizing the outside diameter of the whole lens barrel. Generally, compact DC motors which are employed as the lens driving actuators within the lens barrel of this type are arranged to have their output shafts in parallel to the optical axis of the lens. A reduction gear mechanism is formed by arranging a plurality of spur gears between the output shaft of each of the motors and a focusing-lens or zoom-lens holding tube which is arranged to be driven by the motor.
The diaphragm unit used for the lens barrel of a compact video camera or the like generally consists of a thin cuboid diaphragm mechanism which has a minimal necessary number of blades (two, in most cases) and a driving part which has a braking coil. The diaphragm unit is optically designed to be disposed near the middle part of the lens unit of the lens barrel in general. The layout of the whole lens barrel is as follows: With the diaphragm unit disposed near the middle part of the lens unit, each of the lens driving motors is arranged between the diaphragm unit and an optical focal plane in a small outside diameter part of the lens unit with its output shaft in parallel to the optical axis. Meanwhile, the focusing-lens holding tube and the zoom-lens holding tube which are to be driven by the motors are disposed in front of the diaphragm unit (as viewed on the optical axis). Generally, therefore, the reduction gear mechanism which is provided for reducing the output speed of the lens driving motor is arranged to extend toward the fore end of the lens unit, passing a part near the periphery of the diaphragm unit. The reduction gear mechanism thus engages a large gear disposed on the outer or inner circumferential part of each of the lens holding tubes or transmission tubes. The rotating force of the motor is used for moving the applicable lens through known helicoid and cam mechanisms in the optical axis direction for focusing (focus adjustment) or zooming (power varying).
In accordance with the arrangement of the conventional lens barrel, however, the reduction gear mechanism becomes complex and requires a large space. Besides, the size of the motor is large. Therefore, it has been difficult to make the lens barrel in a compact size and at a low cost. Meanwhile, there is a strong desire for further reduction in size of the video camera. Hence, the size of the lens barrel is also desired to be minimized.